The present invention relates to the fabrication of a fluid ejection device.
A fluid ejection device can be used in printing. An example of the use of a fluid ejection device in printing is a printhead for thermal ink jet printing. Thermal ink jet printing is often accomplished by heating fluid in a firing chamber of a printhead. Typically, the printhead is a semiconductor chip in which there are many firing chambers. The heated ink in each firing chamber forms a bubble. Formation of the bubble forces the heated ink out of a nozzle or orifice associated with the firing chamber towards a medium in a thermal ink jet printing operation. One common configuration of a thermal inkjet printhead is often called a roof shooter-type thermal ink jet printhead because the ink drop is ejected in a direction perpendicular to the plane of the thin films and substrate that comprise the semiconductor chip.
The firing chamber and the nozzles or orifices are typically fabricated in one of two fabrication modes. In the first fabrication mode, the nozzles or orifices are formed in a nozzle plate. The nozzle plate can also be referred to as an orifice layer. The orifice layer can be formed from polyimide or a nickel composition and is situated upon an ink barrier layer that defines the firing chamber. The ink barrier layer is typically composed of an organic material, such as polyimide. In the second fabrication mode, the nozzles or orifices are formed in a single material that is also used to define the firing chamber. This single material can be an organic material, a polymer material, or an organic polymer plastic.
Various problems can occur with respect to the foregoing two fabrication modes for the nozzles and firing chamber. One of the problems arises due to the chemical conditions present in ink jet printing when the firing chamber is fed ink through a slot that originates in the backside of the printhead. The slot is created during fabrication by an etch of the backside of a wafer. The etchant chemistry used to form the slot can have a deleterious effect upon the nozzles or orifices being fabricated, such as over or under etching leading to potential delamination problems.
Other chemically related problems occur in the fabrication of the firing chamber and orifice structures. When the firing chamber and orifice structures are constructed from multiple layers, there are a number of interfaces that are susceptible to chemical attack by the corrosive nature of the ink used in thermal ink jet printing.
In either of the foregoing two fabrication modes, the materials used may not be inherently robust so as to withstand attack from the range of ink chemistries used in thermal inkjet printing. For instance, when a polymer barrier layer is used to define the firing chamber, there can be problems due to the absorption of ink. When the polymer in the polymer barrier layer absorbs ink, the polymer barrier layer tends to swell, chemically degrade, and thermally oxidize or otherwise to form unwanted compounds that are deleterious to the ink jet printhead during field use. When the corrosive ink contacts underlying electrically conductive layers in the printhead, the ink will corrode the conductive layers, resulting in increased electrical resistance and leading eventual failure. In severe cases an entire power supply bus to the printhead may be corroded, resulting in the printhead failing.
Design constraints are often used in the selection of the thickness of the materials that are used to fabricate the nozzles or orifices and the firing chamber in either of the foregoing two fabrication modes. For fluidic reasons, material thicknesses are design constraints that are selected so as to control the volume of a drop of vaporized ink that is ejected out of the nozzle or orifice from the firing chamber. Design constraints can also achieve accurate alignment and placement of the nozzles or orifices in the printhead than can otherwise be achieved by a pick-and-place process using machine vision.
Accordingly, it is desired to protect fluid ejection devices, such as printheads, during fabrication and in the field, and to control the dimensions of the fluid ejection device during fabrication.
In one embodiment, a firing chamber of a fluid ejection device is formed. The firing chamber is substantially defined by a barrier layer and a thin film stack. The barrier layer is formed over the thin film stack. The thin film stack is on a substrate. The thin film stack defines the bottom of the firing chamber. A sacrificial layer is encapsulated between the thin film stack and the barrier layer. The sacrificial layer is removed.
These and other features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.